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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

𝛽−decay of neutron-rich 45 Cl located at the magic number 𝑁 = 28

Results from the β-decay study of 45 Cl, produced in the fragmentation of a 140-MeV/u 48 Ca beam, are presented. The half-life of 45 Cl is measured to be 513(36) ms. β – and β – 1n decay populate excited states in 45 Ar and 44 Ar, respectively, and decay schemes for both daughter nuclei are established based on γ-ray singles and γ-γ coincidence data. Comparison with shell-model calculations using the FSU interaction shows that the low-lying negative-parity states in 45 Ar are well described by single-neutron configurations near the Fermi surface, whereas positive-parity states require neutron excitations across the N = 20 shell gap, consistent with allowed Gamow–Teller decay from 45 Cl. The strong β-feeding to the 5/2 + state in 45 Ar supports a 3/2 + ground-state assignment for 45 Cl over 1/2 + . Furthermore, the high Q β – value enables population of 1p1h states above the neutron separation energy in 45 Ar, leading to positive-parity states in 44 Ar through neutron emission. Tentative spin-parity assignments for excited levels in 44 Ar are made for the first time based on comparison with shell-model predictions, and the 2978-keV level is identified as an excited 0 + state with a configuration distinct from the ground state.

39 ≤ A ≤ 58↗
DOE OSTI2024

Determination of the spins and parities for the 0$^{+}_{4}$ and 0$^{+}_{5}$ states in 100 Zr

Here, two 0 + states at 1294.5 and 1774.0 keV, together with three 2 + and one 4 + levels, were identified or unambiguously spin-parity assigned for the first time in 100 Zr utilizing γ-ray spectroscopy and γ–γ angular correlation techniques with the Gammasphere spectrometer, following the β – decay of neutron-rich, mass-separated 100,100m Y isotopes. Comparisons with recent Monte Carlo shell-model calculations indicate that these two states are candidates for the bandhead of a sequence in a shape-coexisting spherical minimum predicted to be located around ≈1500 keV. According to the measured relative B(E2) relative transition probabilities, the 0$^+_5$ state exhibits decay properties which more closely align with those predicted for a spherical shape, while the 0$^+_4$ level is suggested to be associated with a weakly deformed shape similar to one related to the 0$^+_2$ state.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Nuclear level density and γ -decay strength of Sr 93

This work presents the first experimentally determined nuclear level density and γ-ray strength function of the short-lived fission product 93 Sr, accomplished using the β-Oslo method. Direct measurement of the 92 Sr(n, γ) 93 Sr cross section is not currently possible, as the half-life of 2.66 hours is too short; instead, 93 Sr was formed through β decay of 93 Rb to excitation energies around the neutron separation energy. The γ-ray spectra were measured using a total absorption spectrometer at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). The statistical properties of the 93 Sr nucleus were experimentally determined, including the γ-ray strength function and nuclear level density. At low energies, the γ-ray strength function exhibits a constant γ-decay strength, rather than a slightly increasing strength with decreasing γ-ray energy as had been previously observed for several nuclei in this mid-mass region. Finally, these statistical properties were then implemented in the reaction code TALYS1.95 to calculate the 92 Sr(n, γ) 93 Sr cross section.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Direct observation of 𝛽 and 𝛾 decay from a high-spin long-lived isomer in 187 Ta

187 Ta (Z = 73, N = 114) is located in the neutron-rich A ≈ 190 region where a prolate-to-oblate shape transition via triaxial softness is predicted to take place. A preceding work on the K π = (25/2 - ) isomer and a rotational band to which the isomer decays carried out by the same collaboration revealed that axial symmetry is slightly violated in this nucleus. Here, this paper focuses on a higher-lying isomer, which was previously identified at 2933(14) keV by mass measurements with the Experimental Storage Ring at GSI. The isomer of interest has been populated by a multinucleon transfer reaction with a 136 Xe primary beam incident on a natural tungsten target, using the KEK Isotope Separation System at RIKEN. New experimental findings obtained in the present paper include the internal and external β-decay branches from the high-spin isomer and a revised half-life of 136(24) s. The evaluated hindrances for K-forbidden transitions put constraints on the spin-parity assignment, which can be interpreted as being ascribed to a prolate shape with a five-quasiparticle configuration by model calculations.

beta decay↗
DOE OSTI2025

Multimessengers from the Radioactive Decay of r -process Nuclei

The radioactive β-decay of nuclei synthesized in the rapid neutron capture process (r-process) releases a variety of particles, including electrons, γ-rays, neutrinos, and neutrons. These particles provide a rich set of multimessenger signals that carry information about the astrophysical environments where neutron-rich nucleosynthesis occurs. In this work, we calculate from first principles the emission spectra resulting from the β-decay of r-process nuclei. Our approach incorporates detailed nuclear structure and decay data to model the energy distributions of each particle species. We couple the spectra with a nuclear reaction network simulation to obtain the temporal evolution of these distributions. We find that the emission distributions vary significantly in time and are nonthermal, with substantial average energies. We investigate these nuclear signals as a direct probe of heavy element formation and show that they are complementary observables to kilonova.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Fission Evaluation Tools and Analytics (FETA)

This living document presents the Python package FETA. FETA computes observables resulting from the fission process. This document provides the definition of these observables as well as the physics models that are implemented to compute them. Some of these models are used to determine the initial conditions of fission fragments, e.g., the excitation energy E* and spin distribution p(J, π) at scission for prompt decay, while others are related to the nuclear structure and decay properties of the fragments, e.g. the ground-state properties, level density and low-lying excitation spectrum, γ-strength functions and electromagnetic transitions, and neutron transmission coefficients. The end goal for FETA is to enable users to substitute every one of these models by their own files providing these quantities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

In search of truth: In memory of Balraj Singh

Born in Punjab (India) in December 1941, Balraj Singh is not only the single most prolific nuclear data evaluator and disseminator of nuclear structure and decay data with 148 evaluations in Nuclear Data Sheets — 85 as the first and often only author — plus other journals, but his upmost curiosity and dedication brought him to be one of the finest nuclear physicists, with an everlasting influence on many of us. Furthermore, Balraj passed away about a year ago on 9 October 2023 in Ottawa, Ontario (Canada) at the age of 81, and at Atomic Data and Nuclear Data Tables we would like to commemorate some of his scientific achievements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Determination of the cluster-decay branching ratio from a near-threshold molecular state in Be10

A puzzle has long existed for the α-cluster content in the near-threshold 7.54-MeV state of 10Be. A new measurement was conducted to measure the cluster-decay partial width of this state using the reaction 9 Be( 9 Be, 10 B *→α+ 6 He) 8 Be at 45-MeV beam energy. Special measures were taken to reduce the strong near-threshold background. Additionally, the neutron-decay strength was also obtained based on the threefold coincident measurement. A cluster-decay branching ratio of ( 4.04 ± 1.26 ) × 10 -4 is obtained, resulting in a reasonably large α -cluster spectroscopic factor. The present Rapid Communication confirms the formation of the σ -bond molecular rotational band headed by the 6.18-MeV state in 10 Be .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Identification of new transitions and levels in 163 Gd from $β$-decay studies

Background: Neutron-rich nuclei in the mass region around A = 160 have been and will continue to be of interest for the study of nuclear structure because of the rapid onset of deformation between 88 and 90 neutrons. The observation of detailed changes in nuclear structures within this mass region has provided and will continue to provide insight into the nuclear force. Purpose: Investigations of γ rays emitted following Eu 163 β -decay to Gd 163 have been performed for evaluation of the nuclear structure of Gd 163 . Method: Data were collected at the LeRIBSS station of the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory with an array of four Clover HPGe detectors for γ -rays and two plastic scintillators for β detection. The γ rays were identified as belonging to Gd 163 via mass selection and γ – γ – β , x-ray- γ , or γ – γ coincidences. Results: In total 107 new γ -ray transitions were observed in Gd 163 from 53 newly identified levels. Conclusions: We report the structure of Gd 163 has been identified for the first time. This structure has been evaluated in comparison to projected shell model, and potential energy surface calculations with good agreement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Precise measurements of the γ -ray intensities following the β decay of Ce 144 and Nd 147

For many fission products, the γ rays emitted following β decay provide an easily detectable signature that can be used to identify their quantities and distributions in a sample. As a result, γ-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the γ-ray intensities is available. Further, in many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. In this paper, we present high-precision results for the absolute γ-ray emission intensities for the most intense transitions in the β decays of 144 Ce and 147 Nd. We measured these intensities to ≲1% accuracy by producing radiopure samples with fission-product beams at CARIBU and detecting the emitted radiation with a 4⁢πβ counter and a meticulously efficiency-calibrated high purity germanium detector at Texas A&M University.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Evaluated Nuclear Structure Data File (ENSDF)

Contains recommended nuclear structure and decay data for all the known nuclides, which are obtained following a critical review of all available experimental data, supplemented with systematic trend studies and theoretical models. ENSDF data include (i) nuclear level properties, such as observation source, energy, half-life, decay modes, spin and parity; (ii) gamma ray energies, intensities, multipolarities, mixing ratios and conversion coefficients; (iii) nuclear radiation energy and intensity as well as radiation-specific data for different radiation types, such as such as gammas, alphas, betas and neutrons. Data for about 220 nuclides are fully evaluated each year; additionally, many datasets are partially updated each year. Nearly all the evaluation work is supported by the US Nuclear Data Program. The National Nuclear Data Center at Brookhaven National Laboratory is responsible for coordinating the evaluation effort as well as its web and journal dissemination.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Structure of the high-spin, 𝛽-decaying state in the neutron-rich nucleus 146 La

Excited structures in 146 Ce were populated in 𝛽 decay of the high-spin state in the neutron-rich nucleus 146 La. The beam was produced by the Californium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory, reaccelerated by the ATLAS accelerator, and implanted on a moving-tape system in the middle of the GAMMASPHERE array. The decay scheme of the high-spin, 𝛽-decaying state in 146 La was revised with respect to previous studies and evaluated nuclear data. Here, the structure of 146 La is discussed in the framework of the deformed Nilsson model and systematics of known quasiparticle structures in the region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Determination of the 60 Zn level density from neutron evaporation spectra

Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from β stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus 60 Zn. We have determined the nuclear level density of 60 Zn using neutron evaporation spectra from 58 Ni( 3 He,n) measured at the Edwards Accelerator Laboratory. We compare our results to a number of theoretical predictions, including phenomenological, microscopic, and shell-model-based approaches. Notably, we find the 60 Zn level density is somewhat lower than expected for excitation energies populated in the 59 Cu(p,γ) 60 Zn reaction under rp-process conditions. This includes a level density plateau from roughly 5 to 6 MeV excitation energy, which is counter to the usual expectation of exponential growth and all theoretical predictions that we explore. Here, a determination of the spin distribution at the relevant excitation energies in 60 Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate for the 59 Cu(p,γ) 60 Zn reaction rate at x-ray burst temperatures

59 ≤ A ≤ 89↗
DOE OSTI2020

Covariant density functional theory input for r-process simulations in actinides and superheavy nuclei: The ground state and fission properties

A systematic investigation of the ground-state and fission properties of even-even actinides and superheavy nuclei with Z = 90–120 from the two-proton up to two-neutron drip lines with proper assessment of systematic theoretical uncertainties has been performed for the first time in the framework of covariant density functional theory (CDFT). Furthermore, these results provide a necessary theoretical input for the r-process modeling in heavy nuclei and, in particular, for the study of fission cycling. Four state-of-the-art globally tested covariant energy density functionals (CEDFs), namely, DD-PC1, DD-ME2, NL3*, and PC-PK1, representing the major classes of the CDFT models are employed in the present paper. Ground-state deformations, binding energies, two-neutron separation energies, α-decay Q α values and half-lives, and the heights of fission barriers have been calculated for all these nuclei. Theoretical uncertainties in these physical observables and their evolution as a function of proton and neutron numbers have been quantified and their major sources have been identified. Spherical shell closures at Z = 120, N = 184, and N = 258 and the structure of the single-particle (especially, high-j) states in their vicinities as well as nuclear matter properties of employed CEDFs are two major factors contributing to theoretical uncertainties. However, different physical observables are affected in a different way by these two factors. For example, theoretical uncertainties in calculated ground-state deformations are affected mostly by the former factor, while theoretical uncertainties in fission barriers depend on both of these factors.

190 ≤ A ≤ 219↗
DOE OSTI2020

New transitions and levels for 163 Tb obtained from β-decay studies

Transitions in 163 Tb following β decay of 163 Gd were obtained as part of investigations of γ rays emitted following 163 Euβ decay to 163 Gd. In this work, detailed analysis of the low-energy structure of 163 Tb has been carried out with these data to expand previous β-decay studies and reactions studies of levels in 163 Tb. Data were collected at the LeRIBSS station of the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory with an array of four Clover HPGe detectors for γ rays and two plastic scintillators for β detection. The γ rays were identified as belonging to 163 Gd and 163 Tb via mass selection and γ-γ-β, γ-γ, or γ-x-ray coincidence. In total, 38 new γ-ray transitions were observed in 163 Tb from 15 newly identified levels and 12 previously identified levels. Potential energy surface calculations were performed which support a rigid prolate deformation. Previously identified unplaced transitions in 163 Tb have been placed within the level scheme of 163 Tb and additional states and transitions have been identified.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Mapping of fragmented νf 5/2 →πf 7/2 transitions in the 73 Co→ 73 Ni decay

Excited states in 73 , 75 Ni were investigated through the β decay of 73 , 75 Co in an experiment performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). The experimental results extended the level scheme of Ni 73 to 3.2-MeV excitation energy and provided the experimental information on excited states in Ni 75 . The β -delayed neutron branching ratio for Co 73 was obtained. Furthermore, the experimental results are discussed in comparison with shell-model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗